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Retinal Vein Occlusion
- The Normal Eye
- What is Retinal Vein Occlusion?
- What can you do?
- Who to see and what will happen
- Treatment of Retinal Vein Occlusion
- Experimental treatments for Retinal Vein Occlusion
The Normal Eye [ top ]
The eye is like a camera. Light rays pass through the cornea, the lens and the vitreous to focus on the retina. The cornea is the window at the very front of your eye. The lens is behind the coloured part of your eye (iris). Cloudiness of the lens is called cataract. The vitreous is a jelly-like substance that gives the eyeball its shape and also helps keep the retina intact. Finally, the retina is the tissue at the back of the eye that picks up the light like the film of a camera and transmits it to the brain via the optic nerve. The central part of the retina, which does the straight-ahead vision which is necessary for reading and driving, is called the macula.
What is Retinal Vein Occlusion? [ top ]
The retina has its own blood supply. After entering the eye through the optic nerve, the central retinal artery fans out over the retinal surface. The branch retinal veins collect the blood, forming the central retinal vein, which exits through the optic nerve where it runs side by side with the retinal artery.
Clotting of blood in a retinal vein is a relatively common condition called 'Retinal Vein Occlusion' (RVO). When a retinal vein is occluded, blood returning from the retina that is drained by the vein is blocked, causing the retina to swell, a condition known as retinal oedema. If the retinal vein drains the macula, then macula oedema occurs which causes loss of vision.
The major risk factor for RVO is a history of high blood pressure and vascular disease. It is thought that where the retinal arteries and veins run together (such as in the optic nerve or where they cross in the retina), hardening of the retinal artery (atherosclerosis) squashes the thin walled vein, resulting in a blood clot. Since the retina is actually part of the brain, a retinal vein occlusion can be thought of as a type of stroke.
There are two types of Retinal Vein Occlusion, Branch (BRVO) and Central (CRVO). Both types of occlusion tend to occur suddenly. Both may be either partial ('non-ischaemic' or 'perfused') with relatively normal oxygen levels, or complete ('ischaemic' or 'non-perfused') with low oxygen levels. Visual acuity can range anywhere between and including nearly normal to nearly completely blind when patients are first seen.
BRVO occurs when the obstruction is somewhere in the retina. If the occluded vein does not drain the macula then the patient may not even know it is there. If the macula is involved then vision is blurred and cannot be cleared with glasses
CRVO tends to be more severe than BRVO because the entire retinal circulation is affected in CRVO, not just partially as in BRVO. Macula oedema is almost always present because by definition the whole retina is affected by CRVO
What can you do? [ top ]
There is not much that you can do yourself to treat RVO once it has happened. Fortunately it is uncommon for both eyes to be affected. Since it is regarded as a vascular disease, patients with RVO should review their risk factors for vascular disease with their GP (diet, fitness, weight, smoking, blood pressure etc.). This is more to lower the risk of stroke or heart attack than as a treatment for the retinal condition.
Who to see and what will happen [ top ]
Ophthalmologists (eye doctors) can assess your eyes to look for retinal vein occlusion. You will need a referral to be seen by an Ophthalmologist; your GP, optometrist or specialist can provide this.
On arrival at your ophthalmologist's rooms, you will first be seen by an Orthoptist. The orthoptist will take a history, assess your vision, check your eye pressure, and instill dilation drops to enlarge the pupil, which takes at least another 30 minutes. This will cause your vision to go blurry and light sensitive for several hours after the consultation. It is advised to not drive for approximately two hours after the drops have been instilled and it is also recommended to bring sunglasses.
During your consultation, you may be advised to undergo a fluorescein angiogram. This test involves fluorescein dye, which is injected into the arm causing the dye to travel through the blood vessels to the eye where photos are taken for further assessment. There may be side effects, which will be explained thoroughly at the time. Fluorescein angiograms help the doctor identify the areas of blood leakage and facilitate laser treatment.
Treatment of Retinal Vein Occlusion [ top ]
Retinal vein occlusion often improves without treatment in the first three months, so usually no treatments are applied during that time.
After three months a fluorescein angiogram will be performed (unless the bleeding in the retina is so dense that it obscures what is going on). The angiogram will divide the occlusion into the non ischaemic and ischaemic types. For the non ischaemic types it will also show where the leakage is coming from which is causing the macular oedema.
Laser treatment of BRVO
For non ischaemic BRVO, the standard treatment is with laser. This is usually not dramatically effective, however it is said to improve vision to a certain extent in two out of three treated eyes. Vision rarely returns to normal. Laser treatment of macular oedema in BRVO is essentially the same as laser treatment of diabetic macular oedema; see Diabetes and your Eye
For ischaemic BRVO, if the area affected is large enough then there is a high risk that abnormal new blood vessels will sprout from the affected area and grow into the jelly, or vitreous, where they break and bleed into the eye. This can cause total loss of vision. In order to avoid this, large areas of ischaemia are destroyed with retinal laser treatment. This treatment does not usually improve vision but it is very effective at preventing 'vitreous haemorrhage'.
Laser treatment CRVO
Unfortunately, laser treatment of macular oedema associated with non ischaemic CRVO does not seem to improve vision. So for patients with non ischaemic CRVO there is no proven treatment. Management consists of seeing your eye doctor fairly regularly for the first year or so in order to detect whether it progresses to the ischaemic form, as around 40% do with time. In ischaemic CRVO there is a high risk of blood vessels invading the eye due to the low oxygen levels. These blood vessels grow particularly over the iris (the coloured part of the eye) and into the channels which drain fluid from the eye, resulting in a particularly severe form of glaucoma which, unless it is treated, results in a totally blind, painful eye which often needs to be removed. If your doctor thinks there is a high risk of this happening, he will perform 'pan retinal photocoagulation'; see Diabetes and Your Eye. Laser treatment for proliferative diabetic retinopathy (PRP) is effective in reducing the risk of developing a blind, painful eye, but it does not improve vision.
Experimental treatments for Retinal Vein Occlusion [ top ]
Prof Gillies will discuss the advantages and disadvantages of alternative treatments with you.
Intraocular steroids
The injection of steroids into eyes with retinal vein occlusion can produce quite marked short term improvement in vision by reducing macular oedema. The drug that has been used most commonly so far is 'triamcinolone'. Unfortunately it is still not established whether this treatment leaves eyes better off in the long term. Since there is a high risk of significant adverse events associated with intravitreal triamcinolone treatment such as cataract and glaucoma, the use of intravitreal triamcinolone for retinal vein occlusion can only be performed in certain patients e.g. where there is poor vision in the other eye and preferably the cataract will have been removed from the eye with the vein occlusion.
A new slow-release steroid preparation, 'Posurdex' has been proposed for the treatment of RVO. It might have fewer side effects than triamcinolone. Currently this drug is still being tested and so is only available by participating in clinical trials. Prof Gillies' Clinical Research Unit at the University of Sydney is participating in these and other trials of new treatments for RVO.
Laser-induced Retinal Bypass
Prof Gillies' Clinical Research Unit has recently completed a trial, in collaboration with A/Prof Ian McAllister in Perth, of a new treatment which employs a high powered laser to make a new route of drainage of blood out of the retina. There are risks associated with this treatment as well, including bleeding and scarring inside the eye caused by the laser. Furthermore, the procedure only works in about half the cases in which it is used, but when it does work the results can be very good because the procedure potentially offers an anatomical 'cure' for CRVO. It is anticipated that we will be in a better position to advise patients about the risks and benefits of this study when the results are released towards the end of 2005.
Radial Optic Neurotomy
This procedure, which was devised to decompress the optic nerve in eyes with CRVO, is highly controversial in the United States where it was devised. Most authorities recommend not using it until the results of proper clinical trials are published.
Anti Vascular Endothelial Growth Factor drugs
While these drugs, namely Macugen and Lucentis, hold promise for the treatment of macular oedema associated with RVO in future, at present they are in the early stages of clinical development. A/Prof Gillies may be able to arrange access to these treatments through his Retinal Therapeutics Clinical Research Group at the University of Sydney, which will continue to be a centre in the international trials of these interventions
